Asphalt is one of the world's oldest engineering materials, having been used since the beginning of civilization. Asphalt is a strong, versatile and chemical-resistant binding material that adapts itself to a variety of uses. For example, asphalt is used to bind crushed stone and gravel into firm tough surfaces for roads, streets, and airport runways. Asphalt, also known as pitch, can be obtained from either natural deposits, or as a by-product of the petroleum industry. Natural asphalts were extensively used until the early 1900s. The discovery of refining asphalt from crude petroleum and the increasing popularity of the automobile served to greatly expand the asphalt industry. Modern petroleum asphalt has the same durable qualities as naturally occurring asphalt, with the added advantage of being refined to a uniform condition substantially free of organic and mineral impurities.
Most of the petroleum asphalt produced today is used for road surfacing. Asphalt is also used for expansion joints and patches on concrete roads, as well as for airport runways, tennis courts, playgrounds, and floors in buildings. Another major use of asphalt is in asphalt shingles and roll-roofing which is typically comprised of felt saturated with asphalt. The asphalt helps to preserve and waterproof the roofing material. Other applications for asphalt include waterproofing tunnels, bridges, dams and reservoirs, rust-proofing and sound-proofing metal pipes and automotive under-bodies; and sound-proofing walls and ceilings.
The raw material used in modern asphalt manufacturing is petroleum, which is naturally occurring liquid bitumen. Asphalt is a natural constituent of petroleum, and there are crude oils that are almost entirely asphalt. The crude petroleum is separated into its various fractions through a distillation process. After separation, these fractions are further refined into other products such as asphalt, paraffin, gasoline, naphtha, lubricating oil, kerosene and diesel oil. Since asphalt is the base or heavy constituent of crude petroleum, it does not evaporate or boil off during the distillation process. Asphalt is essentially the heavy residue of the oil refining process.
If asphalt is to be used for a purpose other than paving, such as roofing, pipe coating, or as an under sealant or water-proofing material, the asphalt is usually oxidized, typically by air blowing. Oxidation produces an asphalt material that softens at a higher temperature than non-oxidized asphalts. Oxidation is conventionally done by air blowing at the refinery, at an asphalt processing plant, or at a roofing material plant. Air blowing modifies the asphalt by an oxidation process that involves the blowing of air through the asphalt, either on a batch or continuous basis, with a short residue time at a temperature from 175° C. to 300° C.
While processes for oxidizing asphalt have been commercial for many years, there still remains a need in the art for ever more cost effective processes for modifying the physical properties of asphalt by oxidation.